Aluminum (Al) toxicity is a major agronomic problem on acid soils worldwide, due to increased solubility of Al3+ at a low pH, and inhibition of plant growth. While many crops are tolerant or adaptable to acid soils, important grain crops such as maize are less tolerant and can result in low yields. Within the genetic diversity of maize we see a wide range of tolerance levels to acid soils and aluminum toxicity. This diversity can be used to improve maize cultivars and better understand the genetics and physiology underlying tolerance mechanisms. This thesis provides an overview of Al toxicity and tolerance studies in maize and other crops, as well as novel phenotypegenotype association results in maize. In order to improve crop yields and fertility of cropland a combination of improved genetics, sustainable management practices, and amending of acid soils should be used.